The invention relates to a method of making a hidden tear seam in a vehicle body panel to enable deployment of an airbag via tearing of the panel.
It is well known in motor vehicles to provide an inflatable air bag which is mounted and concealed behind a vehicle body panel.
The vehicle body panel typically includes a rigid substrate panel, a layer of padding material, and a vinyl skin. The substrate material includes an opening which registers with the air bag. A door panel is hinged within the opening and the vinyl material bridges across the opening and the door panel. The prior art is known to promote tearing of the vinyl upon deployment of the air bag by molding the vinyl to provide a reduced cross section thickness of the vinyl skin at the desired location of the tear seam. It has also been proposed to score the vinyl skin using a laser or other cutting technique to weaken the skin and thereby provide a tear seam.
The present invention provides a new and improved process for providing a hidden tear seam in a vinyl skin for an air bag mounted on the steering wheel, on the instrument panel, in the door panel, or elsewhere in the vehicle body.
According to the invention, a method of making a thermoplastic skin comprises the steps of providing a mold having a mold surface with first and second mold surface portions which intersect at a sharp corner coincident with the desired location of the tear seam in the molded skin. The mold is oriented with one of the first and second mold surface portions oriented in a generally horizontally orientation and the other of the mold surface portions oriented in a generally vertical orientation. A thermoplastic material such as polyurethane is sprayed onto the mold surface and the curing of the sprayed material is controlled to permit gravity to induce flow of the sprayed material down the vertical surface of the mold at the sharp corner and thereby provide a cured skin which is of significantly lessened thickness at the corner than at other regions of the skin. Accordingly, the reduced thickness of thermoplastic material at the sharp corner defines the tear seam at which the skin material will tear upon deployment of an air bag against the skin.